Bipedal humanoid robots that can move autonomously while recognizing the surrounding conditions (environment) based upon visual information obtained by a video camera and auditory information obtained by a microphone are known in the art. In a case such as when the movable robot identifies a particular object from the image(s) taken by a CCD camera, for example, parameters regarding imaging sensitivity such as an input gain, white balance setting, etc. can affect significantly to proper image acquisition. Therefore, in order to improve the object identification ability of the robot, it is important to appropriately set the parameters depending on the environment conditions inclusive of the type, brightness, etc. of the light source.
To achieve automatic adjustment of the parameters, Japanese Patent Application Laid-Open Publication No. 2003-289546 (US Publication Number US-2003-0160877-A1) has proposed an imaging device that adjusts the white balance setting by placing a calibration plate in front of the lens at an appropriate timing.
In the prior art technique disclosed in the above publication, however, there is a problem that the robot has to always carry the calibration plate. Also, because the calibration is conducted when the acquired image is found to be unsatisfactory, it is difficult to promptly adjust the parameters to a change in the environment.
Also, it is desired to improve sound-based interactive communication ability of such humanoid robots to increase affinity between robots and people in general life situations and improve work efficiency.
As a sound recognition technique that can be applied to such an interactive communication function, Japanese Patent Application Laid-Open Publication No. 5-134694 has proposed a technique in which when comparing a pattern of sound input to the sound input device with a predetermined reference pattern to detect target sounds or voices, the reference pattern is set to include environmental noise so as to avoid influence from the noise. Japanese Patent Application Laid-Open Publication No. 2000-163098 has proposed to estimate the noise spectrum to eliminate the noise component from the input sound.
However, when the sound recognition is performed on the sound collected by the microphone, which is typically mounted to a head portion of the robot, noises emitted from the robot itself, such as rotation sound of servomotors provided at joints of arms and legs, rotation sound from a cooling fan for an electronic control unit (ECU), operating sounds of other moving parts and sound of footsteps of the robot, can unfavorably influence the sound recognition. For instance, in a robot developed by the assignee of the present application, the sound of footsteps (or the sound generated when the foot hits the floor as the robot walks around) was found to have loudness and waveform similar to those of Japanese casual exclamation of greeting “Oi” uttered from about one meter apart from the robot (see FIG. 5).
Thus, the prior art approach for preventing noise from affecting the sound recognition disclosed in the above publications can be ineffective in coping with irregularly generated noises and/or noises having a similar pattern to that of target sounds, and therefore, adopting the approach may not necessarily lead to more reliable discrimination of a human voice from the surrounding noise.